Transmission of connection set-up parameters in packet data network

ABSTRACT

A method for transmitting connection set-up parameters of a packet data network on broadcast control channels in a telecommunications system which includes at least one cell which uses a circuit-switched broadcast control channel and a packet-switched broadcast control channel. In addition, the telecommunications system includes at least one mobile station which supports the packet data network and is arranged to listen to at least one of the broadcast control channels. The connection set-up parameters of the packet data network are transmitted to mobile stations in the cell on both broadcast control channels, if the cell supports transmitting the connection set-up parameters of the packet data network on both a circuit-switched broadcast control channel and a packet-switched broadcast control channel.

FIELD OF THE INVENTION

The invention relates to packet data services of wirelesstelecommunications systems and especially to transmitting connectionset-up parameters on broadcast control channels.

BACKGROUND OF THE INVENTION

The progress in wireless data transmission has more and more broughtforth the need to transmit wirelessly not only calls but also differentdata applications. The circuit-switched connections used conventionallyin mobile systems are, however, rather poorly suited for transmittingdifferent burst-type data services, which is why packet-switchedapplications have also been developed for mobile systems. During thepast few years, GSM 2+ phase standards, in which the new packet-switcheddata transmission service GPRS (General Packet Radio Service) is alsodefined, have been drafted for the European digital GSM (Global Systemfor Mobile communication) mobile network, for instance. GPRS is a packetradio network utilizing the GSM network, which endeavors to optimizedata packet transmission by means of GPRS protocol layers on the airinterface between a mobile station and a GPRS network.

The GSM system comprises several different, typically unidirectionalcontrol channels, by means of which the network controls the operationof mobile stations. One such channel is the broadcast control channelBCCH, through which information is transmitted on the different cells ofthe network, such as identification information of the cell,identification information on the network, frequencies used in the cell,etc. Each base transceiver station BTS transmits information on a cellon a broadcast control channel of its own, to which all mobile stationsin the area of the cell listen.

Correspondingly, specific control channels have also been designed forthe GPRS system, one of which is the packet broadcast control channelPBCCH, whose task is to transmit system information to all GPRS mobilestations in the cell; just like BCCH does in the GSM network. When aGPRS mobile station is in idle mode, no data transmission resources havebeen allocated to it and it only listens to the broadcast controlchannel BCCH and the paging control channel PCH of the cell, or to thepacket broadcast control channel PBCCH and the packet paging controlchannel PPCH, if the cell supports this GPRS control channel. If thecell does not support this PBCCH channel, which will be a very commonsituation when GPRS networks will be built on top of the GSM network,the GPRS mobile station listens to the GSM broadcast control channelBCCH. The used broadcast control channel, PBCCH or BCCH, is thus definedaccording to which broadcast control channel is available at each timein the cell of the GPRS mobile station.

A GPRS mobile station should thus support broadcast control channelreception on both the PBCCH channel and the BCCH channel. Then, if thecell uses the PBCCH channel, the network transmits the parameters usedin the GPRS network to the mobile stations on said PBCCH channel only.

A problem with the arrangement described above is that if the GPRSmobile station cannot correctly receive system information transmittedon the PBCCH channel, it also cannot transmit or receive data packettransmissions according to GPRS. In the near future, when GSM networkswill be updated to also support GPRS packet data services, a great riskexists that GPRS mobile stations which came out on the market before thePBCCH channel came to the networks will not work on the PBCCH channelsto be built into the networks in the future, because it has not beenpossible to test them in field conditions. Thus, there also exists agreat risk that GPRS mobile stations which came out on the market beforethe GPRS service was initiated will not work in the GPRS network afterthe PBCCH channels are taken into use in the new networks. The extremelysignificant drawback in this is that circuit-switched speech serviceswill not work, either, in such GPRS mobile stations.

BRIEF DESCRIPTION OF THE INVENTION

It is thus an object of the invention to develop a method and anapparatus implementing the method so as to solve the above-mentionedproblems. The object of the invention is achieved by a method and systemwhich are characterized by what is stated in the independent claims.Preferred embodiments of the invention are set forth in the dependentclaims.

The invention is based on the idea that if a cell supports the GPRSservice on both BCCH and PBCCH channels, the network is configured totransmit the parameters required in a GPRS connection to GPRS mobilestations on both broadcast control channels. Such GPRS mobile stationsthat do not work on PBCCH channels to be built into the network,continue broadcast control channel reception only on the BCCH channeland paging reception on the PCH channel and receive through them theparameters required for using the GPRS service in spite of the fact thatthe cell may simultaneously also use a packet broadcast control channelPBCCH.

According to a preferred embodiment of the invention, this can beimplemented by modifying the SI13 message transmitted on the BCCHchannel in such a manner that it indicates that the cell supports thetransmission of the GPRS parameters on both the BCCH channel and thePBCCH channel.

The method and system of the invention provide the advantage that it ispossible to ensure the operation of GPRS mobile stations that come outon the market before the PBCCH channel will be taken in to use, in cellswhich will later on also use a PBCCH channel. A further advantage isthat it is also possible to ensure that GPRS mobile stations to bedeveloped later will also be capable of broadcast control channelreception on the PBCCH channel. A yet further advantage is that thePBCCH channels can be taken into use in GPRS networks as soon as networkmanufacturers can supply them, while at the same time making sure thatthe old GPRS mobile stations still work.

BRIEF DESCRIPTION OF THE FIGURES

In the following, the invention will be described by means of preferredembodiments and with reference to the attached drawings, in which

FIG. 1 shows a block diagram of the structure of the GSM/GPRS system,

FIG. 2 shows a message according to a preferred embodiment of theinvention, and

FIG. 3 shows a message according to a second preferred embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

In the following, the invention will be described by way of examplebased on the GSM/GPRS system. The invention is, however, not limited tothe GSM/GPRS system, but can, for instance, be applied to what is knownas the third-generation mobile system UMTS (Universal MobileTelecommunication System) which comprises functions corresponding to theGPRS system and whose mobile stations should also support the datatransmission of the GSM/GPRS system.

FIG. 1 illustrates how the GPRS system is built on the GSM system. TheGSM system comprises mobile stations (MS) which have a radio connectionto base transceiver stations (BTS). Several base transceiver stationsBTS are connected to a base station controller (BSC) which controls theradio frequencies and channels available to them. The base stationcontroller BSC and the base transceiver stations BTS connected to itform a base station subsystem (BSS). The base station controllers BSCare connected to a mobile services switching center (MSC) which takescare of connection establishment and call routing to correct addresses.In this, two databases containing information on mobile subscribers areused: a home location register (HLR) which contains information on allsubscribers in the mobile network and the services they subscribe to,and a visitor location register (VLR) which contains information onmobile stations visiting the area of a given mobile services switchingcenter MSC. The mobile services switching center MSC is, in turn,connected to other mobile services switching centers through a gatewaymobile services switching center (GMSC) and to a public switchedtelephone network (PSTN). For a more detailed description of the GSMsystem, reference is made to the ETSI/GSM specifications and the bookThe GSM system for Mobile Communications, M. Mouly and M. Pautet,Palaiseau, France, 1992, ISBN:2-957190-07-7.

The GPRS system connected to the GSM system comprises two nearlyindependent functions, i.e. a gateway GPRS support node GGSN and aserving GPRS support node SGSN. The GPRS network can comprise severalgateway and serving support nodes, and typically, several servingsupport nodes SGSN are connected to one gateway support node GGSN. Bothsupport nodes, SGSN and GGSN, act as routers which support the mobilityof the mobile station, control the mobile system and route data packetsto the mobile stations regardless of their location and the usedprotocol. The serving support node SGSN is connected to the mobilestation MS through the mobile network. The connection to the mobilenetwork (interface Gb) is typically established through a base stationcontroller BSC which typically comprises a packet control unit PCU,which creates the function required by the interface Gb in the basestation controller BSC and controls the transmission of data packetsonwards from the base station controller. A task of the serving supportnode SGSN is to detect mobile stations capable of GPRS connections inits service area, to transmit and receive data packets from said mobilestations and to monitor the location of mobile stations in its servicearea. The user data of all GPRS mobile stations in the service area ofthe serving support node SGSN thus goes through said serving supportnode. Further, the serving support node SGSN is connected to a shortmessage switching center SMS-GSMC for incoming short messages through aninterface Gd, and to the home location register HLR through an interfaceGr, and possibly to the mobile switching center MSC and the visitorlocation register VLR through a signaling interface Gs. GPRS recordscomprising the contents of subscriber-specific packet data protocols arealso stored in the home location register HLR.

The gateway support node GGSN acts as a gateway between the GPRS networkand an external packet data network PDN. External packet data networksinclude the GPRS network of another network operator or the Internet.The gateway support node GGSN is connected to said packet data networksthrough interfaces Gp (another GPRS network) and Gi (other PDNs).Private local area networks are typically connected to one of saidpacket data networks through a router. Data packets transmitted betweenthe gateway support node GGSN and the serving support node SGSN arealways encapsulated according to the GPRS standard. The gateway supportnode GGSN also contains PDP (Packet Data Protocol) addresses and routinginformation, i.e. SGSN addresses, of the GPRS mobile stations. Therouting information is used to link data packets between an externaldata packet network and the serving support node SGSN. The GPRS backbonenetwork between the gateway support node GGSN and the serving supportnode SGSN is a network utilizing the IP protocol, either IPv4 or IPv6(Internet Protocol, version 4/6).

The GSM system comprises several different, typically unidirectionalcontrol channels, by means of which the network controls the operationof mobile stations. One of these is the broadcast control channel BCCH,through which information on the different cells of the network, such ascell identification information, network identification information,frequencies used in the cell, etc., are transmitted. Each basetransceiver station BTS transmits the cell information on its ownbroadcast control channel, to which all mobile stations in the area ofthe cell listen. Further, one control channel is a common controlchannel CCCH. CCCH can be divided into three logical channels: a pagingchannel PCH, an access grant channel AGCH and a random access channelRACH. Paging messages to mobile stations, for instance in connectionwith a call set-up initiated by the network, are transmitted on thepaging channel PCH, and on the access grant channel AGCH the basetransceiver station allocates to a mobile station an SDCCH channel forthe allocation of a traffic channel to be used in a call. The structuresof the paging channel PCH and the access grant channel AGCH are alikeand the channels are used in turn according to a certain scheme, i.e.never simultaneously. Said control channels are allocated time divisionframes together with other logical control channels from the samecontrol channel multiframe structure, to which different controlchannels are thus multiplexed as certain channel combinations.

The GPRS system correspondingly has its own packet broadcast controlchannel PBCCH and packet common control channel PCCCH. The task of thepacket broadcast control channel PBCCH is to transmit system informationto all GPRS mobile stations in the cell. Similar to the GSM commonchannel CCCH, the packet common control channel PCCCH comprises severallogical control channels. These include a packet paging channel PPCH,packet access grant channel PAGCH and packet notification channel PNCHin the downlink direction (from the base transceiver station to themobile station), and a packet random access channel PRACH in the uplinkdirection (from the mobile station to the base transceiver station). Thepacket paging channel PPCH is used to transmit paging messages to mobilestations before beginning a data packet transfer, if the location of themobile station is not know at an accuracy of a cell. On the packetaccess grant channel PAGCH, a mobile station is allocated the channelresources available for transfer before beginning a data packettransfer. The packet notification channel PNCH is used to allocateresources for a point-to-multipoint (PTM) message before the PTM messageis transmitted to a certain GPRS mobile station group.

When a GPRS mobile station is in packet-idle mode, no data transmissionresources are allocated to it on the traffic channels and it onlylistens to the packet broadcast control channel PBCCH and packet pagingchannel PPCH of the cell, if the cell supports these GPRS controlchannels. If the cell in question does not support these GPRS controlchannels, said mobile station listens to the GSM control channels BCCHand PCH. The broadcast control channel to be used, PBCCH or BCCH, isthus determined by which broadcast control channel is available at eachtime in the cell of the GPRS mobile station.

If the packet broadcast control channel PBCCH is used, the networktransmits on the PBCCH channel at regular intervals PSI (packet systeminformation) messages which the GPRS mobile station receives regularly.Different types of PSI messages, such as 1, 2, 3, 3bis, 4 and 5, areused on the PBCCH channel. A PSI1 message can also be transmitted on thePPCH channel. From the PSI messages of the PBCCH channel, the mobilestation MS can deduce, whether it can set up a packet data link in thecell in question and what parameters it should use to set up theconnection and to operate in the cell. The most important one of thesemessages is the PSI1 message, by means of which the network notifieswhat the situation is at each time concerning packet data servicesupport and what the sequencing of the PSI messages to be transmittedis. The PSI1 message comprises parameters PBCCH_CHANGE_MARK andPSI_CHANGE_FIELD, by means of which changes occurred in the content,update frequency and deletions/additions of the PSI message can beupdated in such a manner that by increasing the parameter values inconnection with the changes, the mobile stations are directed to updatefrom the network the changed PBCCH values. This way, it is possible toforce all mobile stations in the cell to update their PBCCH informationat the same time.

The broadcast control channel BCCH can be used when the PBCCH channelsis not available in the cell in question or when it is necessary toensure connection to the network in a situation in which PBCCH isremoved for some reason or its location in the cell changes. A mobilestation then listens on the BCCH channel to SI (system information)messages at regular intervals, and especially to the SI13 message whichenables the transmission of the necessary GPRS parameters to mobilestations. The parameters are then transmitted that are required forsetting up a GPRS connection in a cell which has no PBCCH channel. Ifthe cell in question does not support PBCCH, it is possible by means ofthe parameter BCCH_CHANGE_MARK in the SI13 message to update the changesoccurred in the content of the SI messages and to force all mobilestations in the cell to update their BCCH information at the same time.

A GPRS mobile station should thus support broadcast control channelreception on both the PBCCH channel and the BCCH channel. In accordancewith the above, if the cell uses the PBCCH channel, the networktransmits the parameters to be used in a GPRS connection to the mobilestations only on said PBCCH channel. On the other hand, if the GPRSmobile station cannot receive correctly system information transmittedon the PBCCH channel, neither can it transmit or receive a data packettransmission according to GPRS. In such a case, using voice services mayalso be prevented. When the updating of GSM networks is started in thenear future so as to make them also support the GPRS packet dataservice, but only on the BCCH and CCCH channels, a very high risk existsthat GPRS mobile stations which came out on the market at the initialstage of the GPRS service will not work on the PBCCH channels to bebuilt later into the network, since it has not been possible to testthem in field conditions.

This can be avoided in such a manner that if a cell supports the GPRSservice on both the BCCH channel and the PBCCH channel, the network isdirected to transmit the parameters needed for a GPRS connection to GPRSmobile stations on both broadcast control channels. The GPRS mobilestations which do not work on PBCCH channels to be built in the networkthen continue broadcast control channel reception on the BCCH channelonly and paging message reception on the PCH channel, and through themobtain the parameters required for using the GPRS service in spite ofthe fact that the cell may simultaneously also use the packet broadcastcontrol channel PBCCH. All parameters related to the GPRS service aretransmitted on the BCCH channel as if the PBCCH channel was not at allin use. On the other hand, the GPRS mobile stations to be developedlater will also be capable of broadcast control channel reception on thePBCCH channel and packet paging message reception on the PPCH channel.This property, in which the network is capable of transmitting controlcommands related to connection set-up parameters of a packet dataservice on both circuit-switched and packet-switched control channelscan be referred to by the term DCCM (dual control channel mode), forinstance. This way, the PBCCH channels can be taken into use in GPRSnetworks as soon as network manufacturers can supply them, while at thesame time making sure that that the GPRS mobile stations on the marketnow still work. The mobile stations which can change over to receivingthe connection set-up parameters of a packet data service on the PBCCHchannel, even though the network also transmits them on the BCCHchannel, and change over to listening to the PPCH channel, can be calledDCCM mobile stations. Mobile network cells, in which the parametersrelated to the GPRS service are transmitted on both the BCCH channel andthe PBCCH channel, can correspondingly be called DCCM cells.

According to a preferred embodiment of the invention, this DCCM functioncan be implemented by means of the SI13 message transmitted on the BCCHchannel. As shown in FIG. 2, the SI13 message comprises first a 3-bitBCCH_CHANGE_MARK field and after it a 4-bit SI_CHANGE_FIELD field. Thenext bit indicates whether an SI13_CHANGE_MARK field and channelallocation information (GPRS mobile allocation) are transmitted in thismessage. The next bit is used to indicate the broadcast control channelssupported by the cell. The bit value 0 then indicates that the cell doesnot use the packet broadcast control channel PBCCH and the GPRSparameters are only transmitted on the BCCH channel by means of theinformation fields RAC, SPGC_CCCH_SUP, PRIORITY_ACCESS_THR,NETWORK_CONTROL_ORDER, GPRS Cell Options and GPRS Power ControlParameters. The operation of these information fields is not, however,essential for the implementation of the invention and they are describedin greater detail in the document 3GPP TS 04.18, V8.9.0, paragraph10.5.2.37b “SI 13 Rest Octets.”

The bit value 1 is used to indicate that the GPRS parameters aretransmitted in the cell on PBCCH channel only. The parameters aretransmitted by defining the repetition period of the PSI1 message andthe structure of the used PBCCH channel.

Supporting the DCCM operating mode of a cell, in other words,transmitting the GPRS parameters on both the BCCH channel and the PBCCHchannel, can now be arranged by first setting the value of said bit tozero, which indicates that the GPRS parameters are transmitted on theBCCH channel. In addition to this, a new data structure (marked in boldin FIG. 2) is added to the extension part of the message, the datastructure being one that only the GPRS mobile stations which will comeout on the market later on can read and in which the network transmitsthe PBCCH parameters, i.e. information that the PBCCH/PCCCH channels arealso in use in the cell in question, and information on where the PBCCHchannel can be found. Such GPRS mobile stations that do not work on thePBCCH channels to be built into the network then perform broadcastcontrol channel reception on the BCCH channel only and listen to pagingmessages on the PCH channel in spite of the fact that the cell also usesthe packet broadcast control channel PBCCH simultaneously. This meansthat network operators can take PBCCH channels into use in GPRS networksas soon as network manufacturers can supply them.

Thus, by modifying the content of the SI13 message described above, anetwork operator can separately define the use of the BCCH and PBCCHbroadcast control channels in transmitting the GPRS parameters. In thefuture, when the network operator is convinced that substantially allmobile stations in the network operate on the PBCCH channels, the GPRSparameters can then be transmitted on the PBCCH channel only.

If a GPRS mobile station is in packet transfer mode, control messages,PSI messages in particular, can also be transmitted from the network tothe mobile station on a PACCH (packet associated control channel)channel which is an internal control channel, i.e. in-band channel, of atraffic channel PDTCH (packet data traffic channel). In such a case, thecontrol messages are transmitted among the data packets that form theactual payload on the same physical channel. These messages are onlyintended for GPRS mobile stations which can listen to the packet controlchannel, i.e. DCCM mobile stations.

FIG. 3 shows an arrangement according to a preferred embodiment of theinvention, by means of which this reception of PSI messages on the PBCCHand PACCH channels by DCCM mobile stations only can be implemented usingPSI message encapsulation. So that only DCCM mobile stations wouldreceive these messages, but the phones that have come out on the marketearlier would not, PSI messages in a DCCM cell are encapsulated inside aDCCM PSI message. In the message shown in FIG. 3, the type of the PSImessage to be encapsulated is defined in a PSI_MESSAGE_TYPE field andthe actual PSI message to be encapsulated is attached to a PSI_MESSAGEfield. The mobile stations that do not support the DCCM functionalitythen do not recognize the messages and reject them, whereas the DCCMmobile stations recognize them.

A PSI13 message, which is identical to the SI13 message, can also betransmitted on the PACCH channel. If the network makes changes to theinter-allocation of the PBCCH and CCCH channels, it can inform phonesdirectly by transmitting a PSI13 message on the PACCH channel. Thus, ina DCCM cell, it is also possible to update a PSI13 message to correspondto the described content of the SI13 message.

It is obvious to a person skilled in the art that while technologyadvances, the basic idea of the invention can be implemented in manydifferent ways. The invention and its embodiments are thus notrestricted to the examples described above, but can vary within thescope of the claims.

1. A method for transmitting connection set-up parameters of a packetdata network on broadcast control channels in a telecommunicationssystem which comprises at least one cell which uses a circuit-switchedbroadcast control channel (BCCH) and a packet-switched broadcast controlchannel (PBCCH), and at least one mobile station which supports thepacket data network and is arranged to listen to at least one of saidbroadcast control channels, comprising: transmitting the connectionset-up parameters of the packet data network to mobile stations in saidcell on both broadcast control channels in response to the fact that thecell supports the transmission of the connection set-up parameters ofthe data packet network on both the circuit-switched broadcast controlchannel and the packet-switched broadcast control channel; indicatingsaid connection set-up parameters of the packet data network to themobile station in a message which is transmitted on one of saidbroadcast control channels only; wherein said packet data network is aGPRS system; and the GPRS connection set-up parameters are indicated tothe mobile station in an SI13 message which is modified to compriseinformation on the broadcast control channels of the cell that supportthe packet data network and which message is transmitted on thecircuit-switched broadcast control channel; wherein the information inthe SI13 message on the broadcast control channels of the cell thatsupport the packet data network comprises at least one of the following:the cell supports the packet data network on said packet-switchedbroadcast control channel; the cell does not support the packet datanetwork on said packet-switched broadcast control channel; and the cellsupports the packet data network on said packet-switched broadcastcontrol channel and said circuit-switched broadcast control channel. 2.The method as claimed in claim 1, comprising: transmitting to the mobilestations in said cell the control messages to be transmitted on thepacket data network traffic channel (PDTCH) encapsulated inside anothercontrol message in response to the fact that the cell supportstransmitting the connection set-up parameters of the packet data networkon both a circuit-switched broadcast control channel and apacket-switched broadcast control channel.
 3. A telecommunicationssystem which comprises a packet data network and at least one cell whichuses a circuit-switched broadcast control channel (BCCH) and apacket-switched broadcast control channel (PBCCH), and at least onemobile station which supports the packet data network and is arranged tolisten to at least one of said broadcast control channels, in whichtelecommunications system the connection set-up parameters of the packetdata network are arranged to be transmitted on broadcast controlchannels, and the connection set-up parameters of the packet datanetwork are arranged to be transmitted to mobile stations in said cellon both broadcast control channels in response to the fact that the cellsupports transmitting the connection set-up parameters of the packetdata network on both a circuit-switched broadcast control channel and apacket-switched broadcast control channel said connection set-upparameters of the packet data network are arranged to be indicated tothe mobile station in a message which is arranged to be transmitted ononly one of said broadcast control channels; said packet data network isa GPRS system; and the GPRS connection set-up parameters are arranged tobe indicated to the mobile station in an SI13 message which has beenmodified to contain information on the broadcast control channels of thecell that support the packet data network and which message is arrangedto be transmitted on a circuit-switched broadcast control channel;wherein the information contained in the SI13 message on the broadcastcontrol channels of the cell that support the packet data networkcomprises at least one of the following: the cell supports the packetdata network on said packet-switched broadcast control channel; the celldoes not support the packet data network on said packet-switchedbroadcast control channel; the cell supports the packet data network onsaid packet-switched broadcast control channel and said circuit-switchedbroadcast control channel.
 4. The telecommunications system as claimedin claim 3, wherein the control messages to be transmitted on the packetdata network traffic channel (PDTCH) are arranged to be transmitted tothe mobile stations in said cell encapsulated inside another controlmessage in response to the fact that the cell supports transmitting theconnection set-up parameters of the packet data network on both acircuit-switched broadcast control channel and a packet-switchedbroadcast control channel.